VidDownloader (webapp) - When you don't want to mess with installing software to grab that priceless YouTube clip before it gets yanked, head over to web site VidDownloader which sucks in videos from all the big streaming sites (YouTube, Google Video, iFilm, Blip.TV, DailyMotion, etc.), converts 'em for you to a playable format and offers them for download. Other downloaders for online video sites buy you a Flash FLV file, but VidDownloader spits back an AVI file.
http://www.viddownloader.com/